Radio Frequency (RF) shielding may be required on certain semiconductor devices and modules (hereinafter semiconductor device) in order to minimize Electro-Magnetic Interference (EMI) radiation from the semiconductor device. RF shielding is further required to prevent RF radiation from external sources from interfering with operation of the semiconductor device. In a semiconductor device which integrates multiple functions/modules (front end module+transmitter, radio+baseband, etc.) compartmental shielding may be required to minimize EMI radiation from the different components/modules and to prevent RF radiation from interfering with operation of the different components/modules in the semiconductor device.
Presently, there are several different methods used for EMI shielding. A first method is to attach a metal can over the component after the component is attached to the motherboard. An alternative to the shield attached method described above is an embedded EMI shield. In an embedded shield, the metal EMI shield is directly attached to the semiconductor package substrate by means of solder or a conductive adhesive. The shield may be fully embedded within the mold compound of the finished package or can be exposed after assembly. A third method is to apply a conformal shield. In this method, all of the components are placed on the substrate and the substrate, or strip, is over-molded using unit molding, or pin gate molding where individual mold caps are defined within the strip such that upward facing, exposed pads in the substrate remain exposed after the mold operation. A conductive coating is then applied to the strip such that it covers the units and also makes electrical contact to the upward facing pads. The strip is then singulated into individual units. Other methods for providing EMI shielding may use combinations of conformal shields which is applied over a mold cap and makes electrical contact with exposed portions of a wire and or wire fence; exposed metal traces formed through a full or partial saw process, laser ablated vias; and the like.
In general, for a metal can, shield defects may be easily identified by using visual inspection. Visual inspection will show areas on the metal can which are not properly attached to the motherboard and or semiconductor package substrate. However, with conformal shield coatings, visual inspections seldom will catch shield defects. The only reliable way to prove that a semiconductor device with a conformal shield has no shield defects is to treat the semiconductor device as an electrical circuit and to measure the radiated signal level emitted from the body of the semiconductor device. However, presently, there is no device to properly measure the radiated signal level emitted from the body of the semiconductor device under test. This is because it is difficult to distinguish the signal that may be radiating through a defect in the conformal shield since there are multiple signals that may interfere with a proper reading. For example, external noise sources, the signal being emitted through a main antenna port of the semiconductor device, the signal being radiated between the semiconductor device under test and the test board, and the like. All of the above mentioned, interfere with a proper reading of a signal that may be radiating through a defect in the conformal shield.
Therefore, a need existed to provide a system and method to overcome the above problem. The system and method would provide a reliable way of showing if a semiconductor device with a conformal shielding has minimal and or no shield defects.